The goal of this proposal is to develop chemosensors using arrays of engineered yeast strains to mimic olfaction. The experiments I propose will lead to a better understanding of the functional organization and evolution of G protein coupled receptors (GPCRs) and to greater understanding of the molecular mechanisms of olfaction. In many organisms, olfaction appears to be based on a mechanism involving combinatorial activation of broad-specificity GPCRs. I propose to utilize the fundamental mechanisms of olfactory chemosensing to construct yeast arrays capable of serving as chemical sensors. I will take two different approaches to construct the arrays, in each case using yeast strains engineered to functionally express human GPCRs. First, I am currently utilizing directed evolution techniques to generate mutant variants of the human muscarinic and melatonin receptors. I plan to use these mutants to create receptor arrays that are capable of analyzing complex mixtures for low levels of certain analytes. I also intend to continue the efforts of our lab to functionally express olfactory receptors in yeast. I will analyze libraries of chimeras between the melatonin receptor and olfactory receptors with known ligands. Once functional receptors are isolated, I plan to develop a generalized technique for generating functional chimeric olfactory receptors.